1. Field of the Invention
The present invention relates to substrate-guided optical devices, and particularly to devices which include a plurality of reflecting surfaces carried by a common light-transmissive substrate, also referred to as a light-guide element.
The invention can be implemented to advantage in a large number of imaging applications, such as head-mounted and head-up displays, cellular phones, compact displays, 3-D displays, compact beam expanders, as well as non-imaging applications like flat-panel indicators, compact illuminators and scanners.
2. Description of Related Art
One of the important applications for compact optical elements is in head-mounted displays where an optical module serves both as an imaging lens and a combiner, in which a two-dimensional display is imaged to infinity and reflected into the eye of an observer. The display can be obtained directly from either a spatial light modulator (SLM) such as a cathode ray tube (CRT), a liquid crystal display (LCD), an organic light emitting diode (OLED) array, or a scanning source and similar devices, or indirectly, by means of a relay lens or an optical fiber bundle. The display comprises an array of elements (pixels) imaged to infinity by a collimating lens and transmitted into the eye of the viewer by means of a reflecting, or partially reflecting surface acting as a combiner for non-see-through and see-through applications, respectively. Typically, a conventional, free-space optical module is used for these purposes. As the desired field-of-view (FOV) of the system increases, however, such a conventional optical module becomes larger, heavier and bulkier, and therefore, even for a moderate performance device, is impractical. This is a major drawback for all kinds of displays, but especially in head-mounted applications, where the system must, of necessity, be as light and as compact as possible.
The strive for compactness has led to several different complex optical solutions, all of which, on the one hand, are still not sufficiently compact for most practical applications, and, on the other hand, suffer major drawbacks in terms of manufacturability. Furthermore, the eye-motion-box (EMB) of the optical viewing angles resulting from these designs is usually very small, typically less than 8 mm. Hence, the performance of the optical system is very sensitive, even to small movements of the optical system relative to the eye of the viewer, and does not allow sufficient pupil motion for convenient reading of text from such displays.
For a more detailed background of the present invention, the teachings included in the publications WO 01/95027, WO 03/081320, WO 2005/024969, WO 2006/013565, WO 2006/085309, WO 2006/085310, WO 2007/054928 and PCT/IL2007/000172 in the name of Applicant, are herein incorporated by references.